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NASA's Chandra X-ray Observatory located a cosmic "ghost" that scientists think is evidence of a huge eruption produced by a supermassive black hole equal in power to a billion supernovas. The source, HDF 130, is over 10 billion light years away and existed at a time 3 billion years after the Big Bang, when galaxies and black holes were forming at a high rate. The X-ray ghost, so-called because a diffuse X-ray source has remained after other radiation from the outburst has died away, is in the Chandra Deep Field-North, one of the deepest X-ray images ever taken.

"We'd seen this fuzzy object a few years ago, but didn't realize until now that we were seeing a ghost", said Andy Fabian of the Cambridge University in the United Kingdom. "It's not out there to haunt us, rather it's telling us something - in this case what was happening in this galaxy billions of year ago."

Fabian and colleagues think the X-ray glow from HDF 130 is evidence for a powerful outburst from its central black hole in the form of jets of energetic particles traveling at almost the speed of light. When the eruption was ongoing, it produced prodigious amounts of radio and X-radiation, but after several million years, the radio signal faded from view as the electrons radiated away their energy.

However, less energetic electrons can still produce X-rays by interacting with the pervasive sea of photons remaining from the Big Bang - the cosmic background radiation. Collisions between these electrons and the background photons can impart enough energy to the photons to boost them into the X-ray energy band. This process produces an extended X-ray source that lasts for another 30 million years or so.

"This ghost tells us about the black hole's eruption long after it has died," said co-author Scott Chapman, also of Cambridge University. "This means we don't have to catch the black holes in the act to witness the big impact they have."

This is the first X-ray ghost ever seen after the demise of radio-bright jets. Astronomers have observed extensive X-ray emission with a similar origin, but only from galaxies with radio emission on large scales, signifying continued eruptions. In HDF 130, only a point source is detected in radio images, coinciding with the massive elliptical galaxy seen in its optical image. This radio source indicates the presence of a growing supermassive black hole.

"This result hints that the X-ray sky should be littered with such ghosts," said co-author Caitlin Casey, also of Cambridge, "especially if black hole eruptions are as common as we think they are in the early Universe."

"Even after the ghost disappears, most of the energy from the black hole's eruption remains", said Fabian. "Because they're so powerful, these eruptions can have profound effects lasting for billions of years."

Astronomers have discovered a potentially habitable planet of similar size to Earth in orbit around a nearby star.

A team of planet hunters spotted the alien world circling a red dwarf star called Gliese 581, 20 light years away.

The planet is in the "Goldilocks zone" of space around a star where surface temperatures are neither too hot nor too cold for liquid water to form.

"Our findings offer a very compelling case for a potentially habitable planet," said Steven Vogt, an astronomer at the University of California, Santa Cruz. "The fact that we were able to detect this planet so quickly and so nearby tells us that planets like this must be really common."

If confirmed, the planet would be the most Earth-like that has ever been discovered in another solar system and the first strong contender for a habitable one.

More than 400 exoplanets have been discovered by astronomers, but most are gas giants, like Jupiter, that would be inhospitable to life as we know it.

Astronomers used the Keck telescope in Hawaii to study the movement of Gliese 581 in exquisite detail and from their observations inferred the presence of a number of orbiting planets. The team report two new planets in the Astrophysical Journal, bringing the total number known to be circling the star to six.

One of the planets, named Gliese 581g, has a mass of three to four times that of Earth and takes 37 days to orbit the star. Astronomers believe it is a rocky planet with enough gravity to retain an atmosphere.

Unlike the previously discovered planets, Gliese 581g lies squarely in the region of space were life can thrive. "We had planets on both sides of the habitable zone — one too hot and one too cold — and now we have one in the middle that's just right," Vogt said.

One side of the planet is always facing the star, much as one side of the moon constantly faces Earth. This means that the far side of the planet is constantly in darkness. The most habitable region of the planet would be the line between the light and dark regions.

"Any emerging life forms would have a wide range of stable climates to choose from and to evolve around, depending on their longitude," Vogt said.

The average temperature on the planet is estimated to be between -31 to -12C, but the ground temperature would vary from blazing hot on the bright side and freezing on the dark side.

"The number of systems with potentially habitable planets is probably on the order of 10 or 20 percent, and when you multiply that by the hundreds of billions of stars in the Milky Way, that's a large number. There could be tens of billions of these systems in our galaxy," said Vogt.

i was all anxious and nervous when the balloon burst. i was like, "gah! it's covering up the camera! i wanna see the descent!" yes, i'd love to do something like that. my friends and i are always looking for fun projects to throw ourselves into (currently writing a movie), but something like this would totally appeal to the severe geekiness in us all!

The GL581 result bothers me. There are lots of quotes floating around from Vogt that say he's "100% certain" that there is life on the newly discovered planet, which was obviously meant just to sensationalize the story for the press. Almost nothing in science is 100% certain. The detection of that planet isn't 100% certain. This is the 7th planet they think they've detected, and who knows if the perturbations from the other 6 are contributing to a pattern they don't understand, rather than the pattern being a real detection of a 7th planet. The mass of the planet is also uncertain; models for planet masses produce notoriously large error bars. Additionally, GL581 is not a solar analogue - it's an M dwarf. What life would be like around such a low mass, low temperature star, we don't know. And the planet is said to be tidally locked - one dark side and one light side. So if water/life exists, does it only exist in the 'dawn' and 'dusk' areas on the planet? Also unknown. I would think the formation of life in such a narrow band would improbable.

I understand the need to have the public excited and informed about astronomy. I really do. But this missed the mark for me, and I think there is a bit of politics involved between the major players in this field that is influencing the way this was released.